HIV aikidoka (or senseis)
Though I never had to train with someone with HIV (unless I didn't know they had it), I don't think I'll have any problem with it. They are just normal people and the only reason for concern is blood mixing with blood. And thanks but I don't see alot of that happening in training.So, actually there is hardly a chance for such a thing to happen, and if someone bleeds, there is no problem to clean it up without touching the blood.
I think everyone should get a fair chance to train.
The problem might start if someone else in the dojo thinks differently, then the situation would be 'me or him', which could lead to an uncomfortable situation. Still, I think an HIV person should be let in the dojo, actualy, if such a situation would arise, I wouldn't like to train with someone who will say 'him or me'.
Hope people in aikido are more grown up to see the reason behind letting a person train or not, and not let superstition rule.